ACL-Based Forwarding (ABF) is a type of routing which makes decisions based on whether or not a packet matches a Standard Access List (ACL). This type of routing is also commonly called Policy-Based Routing (PBR).
ABF can make routing decisions based on any property of a packet that an ACL is capable of matching. It could be a source address, a specific TCP port, a specific protocol, or combination of those properties, such as traffic matching both a specific source and destination address.
Traditional routing, such as from static routes or dynamic routing protocols use the routing table to decide where to send traffic based on where the traffic is going, meaning the destination address of a packet. Multiple routing tables (via VRF) can allow some differences on a per-interface level but it’s as flexible as ABF.
The downside is that processing ABF policies consumes more resources than traditional routing. The exact difference in performance will vary by platform.